Resistive position indicator

ABSTRACT

Resistive position indicator has an enlongated resistive element with an electrical terminal at each end and a tap which can be brought into contact with the resistive element. A contact point divides the resistive element into two portions and is movable along the resistive element, so that the resistance ratio between the two portions of the resistive element can be varied within wide limits. The resistive element consists of a layer of resistive material applied on a substrate of electrically insulating material. The tap comprises an elongated contact portion of electrically conducting material applied on a substrate and positioned in front of, parallel to, and slightly spaced from the resistive element, so that an air gap is formed between the resistive element and the contact portion of the tap. At least one substrate consists of a flexible foil, so that the air gap between the resistive element and the contact portion of the tap can be eliminated at any point along the resistive element by a compressive force on the flexible foil, so that the contact portion of the tap is brought into contact with the resistive layer at that point. The substrates can be a continuous strip of flexible foil which is folded and provided with an insert of insulating material having a slot. The position indicator has low friction, a low weight, and requires little space.

TECHNICAL FIELD

The present invention relates to a resistive position indicatorcomprising an elongated resistive element having an electrical terminalat each end and a tap means which can be brought into contact with theresistive element. The contact point of the tap means divides theresistive element into two portions and is movable along the resistiveelement, so that the resistance ratio between the two portions of theresistive element can be varied within wide limits. The positionindicator is primarily intended for use in motorized height adjustersfor the pillar loop in vehicle safety belts but can also be used in manyother devices, e.g. in electrical regulating and controlling equipment.

BACKGROUND ART

Resistive position indicators designed as slide rheostats and rotatingpotentiometers are previously well known. However, in these indicators amovable tap means is used which abuts against a normally coiledresistive wire or a resistive layer and is moved over the wire turns orthe resistive layer when adjusted. This gives a comparatively highfriction which causes a heavy wear and a reduced reliability and whichalso makes the adjustment of the indicator more difficult. Furthermore,these prior art indicators have a comparatively high weight and acompartively large required space.

SUMMARY OF THE INVENTION

The main object of the invention is to provide a resistive positionindicator having a substantially lower friction when adjusted than theresistive position indicators of the prior art and also having anextremely low weight and a small required space. According to theinvention, this object is achieved by giving the resistive positionindicator the features set forth in the claims.

Due to the fact that the tap means comprises an elongated contactportion positioned in front of the resistive element and slightly spacedfrom this element, so that an air gap is formed between the resistiveelement and the contact portion of the tap means, and due to the factthat the air gap can be eliminated at any point along the resistiveelement by a compressive force, there is no means to be moved on theresistive element. This will reduce the friction substantially. Due tothe fact that the compressive force can be applied on a flexible foil,only a small compressive force is required to provide the necessarycontact between the resistive element and the contact portion of the tapmeans. Furthermore, the means providing the pressure can slide on thesurface of the foil which can be made very smooth, so that the frictionwhen the indicator is adjusted is further reduced. This is a substantialimprovement over the resistive indicators of the prior art in which thecontact portion of the tap means slides on a resistive surface havinghigh friction.

Particularly, if both the resistive element and the contact portion ofthe tap means are applied on flexible foils, which can be made verythin, a very thin position indicator is obtained, which has a very smallrequired space and which due to its flexibility easily can be positionedin narrow spaces. In this case, the indicator will also get a very lowweight.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of a resistive position indicator according to theinvention will now be further described below with reference to theaccompanying drawings.

FIG. 1 shows a resistive position indicator, formed on a flexible foilstrip, before the final assembly.

FIG. 2 is a cross section through the position indicator according toFIG. 1 after the final assembly.

FIG. 3 is a cross section through a height adjuster for the pillar loopin a vehicle safety belt, the height adjuster being provided with aresistive position indicator according to FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The resistive position indicator shown in FIG. 1 comprises an elongatedstrip 10 of flexible plastic foil. The strip is divided into twoportions 10B and 10C of substantially equal length by two notches 10A.The strip is further provided with an angularly projecting extension 10Dpositioned at the end 10E of the portion 10B turned away from theportion 10C.

Strip 10 has first, second, third, and fourth areas or layers ofmaterial 11, 13, 14, and 12 as follows. The first area or thin layer 11of a material having high resistivity is applied on the strip 10. Thefirst layer is positioned on the longitudinal central axis of the stripand runs along substantially the full length of the first portion 10B ofthe strip. The first area or layer is at its ends connected toelectrical conductors 12 and 13 consisting of fourth and second areas orthin layers of a material having low resistivity. The conductor 12 runsstraight to the extension 10D of the strip, while the conductor 13 firstruns parallel to the resistive layer 11 on the strip portion 10B toopposite end of the resistive layer and then enters the extension 10D ofthe strip. The strip 10 is provided with a further electrical conductor14 consisting of a layer of a third area or material having lowresistivity. The conductor 14 runs along the full length of the strip 11from the free end 10F of the strip over the portions 10C and 10B to theend 10E, where it enters the extension 10D. On the strip portion 10C theportion 14A of the conductor runs on the longitudinal central axis ofthe strip. On the strip portion 10B the portion 14B of the conductorruns parallel to the resistive layer 11 on the opposite side of thatlayer in relation to the connecting conductor 13 of the resistive layer.

The strip is intended to be folded 180° at the notches 10A, so that theportion 10C of the strip will be positioned straight over the portion10B and the conductor 14A on the portion 10C will be positioned straightover the resistive layer 11, as shown in FIG. 2. When the strip isfolded, a thin insert 15 of a flexible, electrically insulating materialis applied between the two portions 10B and 10C of the strip which areglued together. The insert is provided with a slot 16, the width andlength of which correspond to the resistive layer 11. The insert has thesame width as the strip 10 and is preferably made of the same foil asthe strip 10. The purpose of the insert is to prevent direct contactbetween the conductor 14A of the portion 10C and the resistive layer 11.Thus, the insert 15 will form an air gap 16A between the resistive layer11 and the conductor 14A of the portion 10C, when the strip portion 10Cduring the folding of the strip 10 is positioned on top of the stripportion 10B, as shown in FIG. 2. The strip extension 10D carrying theconductors 12, 13 and 14 is provided with electrical terminals (notshown) for the conductors, so that the position indicator can beconnected to a control circuit.

FIG. 3 shows the resistive position indicator applied in a heightadjuster for the pillar loop for the strap in a safety belt. The heightadjuster comprises a bar 17 which has a substantially U-shaped crosssection and in which a carrier 18 for the pillar loop 19 for the strapof the safety belt is movably mounted. The carrier 18 is mounted on arotatable spindle 20 provided with external threads cooperating withinternal threads in a through hole 21 in the carrier, as schematicallyindicated in FIG. 3. The spindle 20 is connected to a motor (not shown)which can cause the spindle to rotate to move the carrier in theU-shaped bar. A height adjuster of this type is disclosed in greaterdetail in Swedish Patent Application No. 8505832-9.

For an automatic adjustment of the height adjuster, e.g. depending on astored code for a particular driver, a position indicator is requiredwhich indicates the actual position of the carrier 18 in the heightadjuster, so that the carrier can be brought to the desired position.The resistive position indicator according to the invention is appliedin the bar of the height adjuster for this purpose, as will be furtherdescribed below.

The folded strip 10 is attached to the inner side of a side portion 17A.Due to the angular shape the extension 10D of the strip can bepositioned along the bottom portion 17B of the bar for connection toexternal lines. The carrier 18 is on the side 18A facing the strip 10provided with a hole 22, which is not a through hole and which runsperpendicularly from the surface of the side towards the longitudinalcentral plane 23 of the carrier. A compression spring 24 is applied inthis hole, and one end of the spring abuts against the bottom of thehole and the other end abuts against a pressure element 25 movablymounted in the hole and partially projecting in front of the side 18A ofthe carrier. The pressure element 25 is so designed that its projectingportion abuts against the strip 10, more particularly against the backside of the strip portion 10C, and forces the conductor 14A against theresistive element 11 at this point. In this position the pressureelement 25 is slightly pushed into the hole 22, so that the pressureelement is forced by the spring 24 towards the strip 10 to secure acertain contact pressure between the pressure element and the strip 10.

The position indicator in the height adjuster operates in the followingway. In operation the resistive layer 11 is connected to a voltagesource by means of its connecting conductors 12 and 13, so that avoltage is applied over the resistive layer. When the carrier 18 ismoved in the bar 17 by means of the spindle 20, the pressure element 25in the carrier will be moved on the strip 10, so that the contact pointbetween the conductor 14A and the resistive layer 11 also will be movedalong the resistive layer. The voltage which can be tapped from theconductor 14 at its terminal point on the extension 10D of the stripwill then vary in relation to the movement of the carrier, so that theobtained voltage can be used to indicate the actual position of thecarrier in the bar. The obtained voltage can vary between zero and thepeak voltage over the resistive layer supplied by the connected voltagesource, depending upon the resistance ratio between the two portions ofthe resistive layer on either side of the contact point between theconductor 14 and the resistive layer 11 established by the pressureelement 25 in the carrier 18.

While only one embodiment of the resistive position indicator accordingto the invention has been described above and shown on the drawings, itis evident that many variations and modifications are possible withinthe scope of the invention. The strip does not have to consist of acontinuous flexible foil, and the substrate carrying the resistive layerand the conductors may consist of several separate parts. If so, onlyeither the substrate of the resistive layer or the substrate of theportion of the tapping conductor to be brought into contact with theresistive layer needs to be of a flexible material that can be actuatedby a pressure element. The insert between the resistive layer and thecontact portion of the tapping conductor can also be designed in severalways and may possibly be replaced by a lowering of either the resistivelayer or the contact portion of the tapping conductor in the pertainingsubstrate. The insert can also consist of a double-faced tape, so thatthe insert produces the connection of the substrates. The resistivelayer and the conductors can also be positioned in several ways on thesubstrate or substrates. The layer and the conductors do not have to belinear but can be of any shape, e.g. curved. The position indicator canthen easily be adapted for use in different fields. The contact portionof the tapping conductor does not have to be provided with an electricalterminal, but the contact portion can be adapted to be brought intocontact with a conducting layer having low resistivity positioned on thesame substrate as the resistive layer and provided with an electricalterminal. The contact portion will then exclusively work as a contactbridge. The resistive layer must have a subtantially higher resistivitythan the conductors, but many different resistivity values are possiblefor the resistive layer as well as for the conductors. The thickness andwidth of the layers can also be changed within wide limits. If thecontact portion of the tapping conductor does not work exclusively as acontact bridge, it is convenient that the resistive layer has a largerwidth than the contact portion of the tapping conductor, so that therequired accuracy at the folding of the strip or at the connection ofthe substrates will not be too high. The terminal points of the positionindicator do not necessarily have to be positioned at one end of theposition indicator or not even adjacent each other, but it is easier toconnect the external lines, if the terminal points are positionedadjacent each other.

What is claimed is:
 1. A resistive position indicator comprising: aninsulating substrate; a first area of conductive material on saidsubstrate comprising an elongated resistive element; a second area ofconductive material on said substrate comprising an elongated conductor,extending substantially parallel with said resistive element, and beingconnected thereto at one end; a respective terminal provided at theother end of said resistive element and of said conductor adjacent oneend of said substrate; a third elongated area of conductive material onsaid substrate, extending substantially parallel with said first andsecond areas and having a terminal at the same end of said substrate asthe other terminals; a tap means, connected to said third area, forcontacting said resistive element at a contact point which is movablealong the resistive element and divides the resistive element into twoportions so that the resistance ratio between the two portions of theresistance element can be varied between wide limits, said tap meansincluding an elongated area of low resistivity electrically conductingmaterial which is applied to an insulating supporting substrate,extending parallel to and slightly spaced from said substrate carryingsaid first, second, and third areas of conductive material, and whichhas a contact portion positioned in front of, parallel to, and slightlyspaced from said resistive element and defining an air gap between saidresistive element and said contact portion; and at least one of saidsubstrate and said supporting substrate consisting of a flexible foil sothat adjacent points on said contact portion of said tap means and onsaid resistive element can be brought into contact, and close said airgap between said resistive element and said contact portion, at anypoint along said resistive element by means of a compressive force onsaid flexible foil to establish said contact point.
 2. A resistiveposition indicator according to claim 1, wherein said first area formingsaid resistive element is centrally disposed between said second andthird conductive areas, and further comprising insulating means disposedbetween said second and third conductive areas and said supportingsubstrate carrying said tap means.
 3. A resistive position indicatoraccording to claim 2, wherein said substrate and said supportingsubstrate consist of different portions of a single flexible foil strip,said flexible foil strip is folded back on itself between said twoportions, so that said two portions of said strip face each other, andsaid tap means, on one portion of said strip, is formed integrally withsaid third conductive area which is formed on the other portion of saidstrip.
 4. A resistive position indicator according to claim 2, whereinsaid insulating means comprises an insert of flexible insulatingmaterial disposed between said insulating substrate and said insulatingsupporting substrate, said insulating insert having an elongated slottherein between said resistive element and said contact portion of saidtap means.
 5. A resistive position indicator according to claim 1,wherein said substrate and said supporting substrate consist ofdifferent portions of a single flexible foil strip, said flexible foilstrip is folded back on itself between said two portions, so that saidtwo portions of said strip face each other, and said tap means, on oneportion of said strip, is formed integrally with said third conductivearea which is formed on the other portion of said strip.
 6. A resistiveposition indicator according to claim 1, wherein each one of saidinsulating substrate and said insulating supporting substrate is aflexible foil.
 7. A resistive position indicator according to claim 6,wherein each one of said insulating substrate and said insulatingsupporting substrate is a different portion of an integral flexiblefoil, and said integral flexible foil is folded 180 degrees so that saidinsulating and insulating supporting substrates face each other.
 8. Aresistive position indicator according to claim 6, wherein saidresistive element is broader than said contact portion of said tapmeans, and said flexible foil comprising said insulating supportingsubstrate is adapted to be forced against said flexible foil comprisingsaid insulating substrate for establishing the contact between saidcontact portion and said resistive element at said contact point.